The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Various nitrogen oxides, such as nitric oxide (NO) and nitrogen dioxide (NO2), which may be generally be referred to as NOx, as well as sulfur oxides (SOx), particulate matter (PM) and carbon dioxide (CO2) represent the types of air pollution formed upon the combustion of hydrocarbon fuels. The nitrogen oxides (NOx) are formed by the reaction of nitrogen and oxygen at the relatively high temperatures generated during the combustion process. The emission of sulfur oxides (SOx) are due to the presence of various sulfur compound as impurities in the hydrocarbon fuel. The air pollution arising from fuel combustion contains gases that are hazardous to human health, as well as gases that have a greenhouse effect on the environment.
Selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) reduce post combustion NOx by reacting the exhaust gases with urea or ammonia to produce nitrogen and water. SCR is now being used in many applications, including the treatment of exhaust gases in ships, diesel trucks and in some cars. The use of exhaust gas recirculation and catalytic converters in motor vehicle engines have significantly reduced vehicular emissions.
In addition, to the catalytic conversion of NOx and SOx gases to other compounds, current emission control technology also utilizes various active and passive absorbers to trap or bind NOx and/or SOx. For example, NOx storage and reduction (NSR) catalysts are run cyclically under a lean environment (oxidizing) and rich environments (reducing) as determined by the corresponding ratio of air to fuel.
Global emission regulations are trending towards the decrease in allowable NOx emissions. Current and future regulations are decreasing the amount of allowable NOx emissions that may be present in an exhaust gas by 90% or more. Over 75% of the NOx emissions from the tail pipe of a vehicle result during cold start, which leads to a requirement of increased NOx trapping capacity over the catalyst activity without increasing the overall volume of the catalyst present. Thus, catalysts formed with or on oxide support materials that meet the requirements of these new regulations with enhanced capability for NOx or SOx trapping is desirable.